UK light-heavyweight Buatsi earned a win yet disappointing debut to his career under recent management with a points victory over Parker in the Manchester arena.
The Olympic bronze medallist's punch output appeared to earn him a judges' verdict in a tight 10-round bout at the boxing arena.
But Parker landed significant shots, connecting with powerful clean blows in a contest where the styles didn't complement each other, with frequent clinching spoiling the contest.
The officials judged it 96-94 for to the winner, with the third a even score.
"It wasn't my greatest performance but what defines champions? They prevail," Buatsi commented in the ringside as he was met by negative reactions from the audience.
The Londoner got back to winning after his maiden career setback - an epic battle with Callum Smith in February - to secure a twentieth professional win.
Some ringside observers thought Parker, thirty-one, merited the win but the British boxer suffered the second setback of his 28-match career.
Buatsi Earns Victory in Uneventful Match
Buatsi's progress has stalled in recent years through contract problems and long spells of inactivity.
Previously predicted as the future of British boxing, he now is positioned trying to fulfil that early promise - perhaps in what appears to be a ultimate opportunity - under new promotional backing.
He started carefully, with both competitors ready to take risks in a calculated initial rounds.
The challenger, whose sole prior loss came at the lower weight class against John Ryder in two years ago after damaging his hand mid-fight, was competing in only his second bout at light-heavyweight.
By the halfway stage, Parker had kept it close, causing problems for the favorite, who worked behind a tight guard to narrowly win the cleaner rounds.
The crowd's patience decreased during constant clinching, with Parker slipping to the canvas various instances during grappling.
The underdog closed well, but multiple periods were hard to judge. However, previous titleholder the boxing analyst - working with Dazn - had it particularly wide for the challenger, awarding Buatsi just one round.
The victor moves on, but with the presence of hard hitter David Benavidez, and Russian star Bivol leading the category, the path to championship success - on this evidence - still seems difficult.
Hatton Homage Fuels All-Manchester Fight
In the co-main event, Lyndon Arthur beat Bradley Rea by divided decision in a terrific Manchester vs Manchester contest to win the European light-heavyweight belt.
The stadium grew hushed for a profoundly moving memorial prior to the bout as ten bells sounded in remembrance of local hero Hatton, who succumbed 46 years old in September.
It was the initial significant broadcast match card in the location since the passing of Hatton. As the concluding sound faded, the stillness transitioned to a shout of "there's only one Ricky Hatton".
The fighting within the ring reflected the sentiment. Arthur was knocked down by a powerful punch flush on the face in the second round, standing uncertainly to his feet on the count of eight.
But the traditional red shorts of Arthur soon pressed ahead again. On the opposite side, the opponent - in rival City blue - was injured soon, noticeable damage appearing under his face as the fighters landed hard punches.
The challenger, 27, delivered effective strikes but Arthur, 34, responded in kind with stinging uppercuts as the intensity hardly diminished over 12 rounds.
The victor edged the verdict with scoring tallies of even score, narrow lead and 115-112, but the two athletes were persistent and full of heart, exactly what their inspiration the legend represented.
